This invention relates to the field of collators and to the construction of a collator bin, this construction being such as to facilitate the stacking of a large number of sheets into a compact space.
As is well known to those in the art, cut paper is received from the manufacturer in stacks, all sheets having the more dense and smooth felt side facing one direction and the wire side facing the other direction. Generally, the sheets are cut grain-long. That is, the longest sheet dimension is aligned with the paper's grain fibers. As a result, the paper tends to curl in its shortest dimension, or cross-grain. Paper manufacturers generally recommend that printing be placed on the felt side.
Most methods of printing, and particularly the xerographic method of printing wherein loose toner is melted or fused onto the paper, result in the heating and drying of the printed sheet. As is also well known, this heated paper tends to curl toward the wire side of the sheet. This curl causes the sheet to assume a cylindrical concave shape, curled along its longest dimension, due to it being cut grain-long.
By way of example, sheet curl, measured from the plane of its upturned edges to a parallel plane cutting the apex of its curl, is from 0.2 to 0.6 inch. Greater curl is experienced with paper of higher moisture content.
Prior art collating apparatus generally provide a plurality of horizontal or vertically stacked bins, whose sheet holding capacity is restricted by the size of each individual bin, and by the ability to insert a sheet into the bin without jamming the leading edge of that sheet against the trailing edge of the sheets already stacked in the bin. Various means such as flaps and wire guides are provided in the prior art to hold down the trailing edge of the sheets already in the bin, so as to allow the leading edge of the subsequent sheet to enter the bin without a jam.
The present invention is directed to the vertical stacking of sheets which have a tendency to curl in a collator bin having a small finite capacity. Stacking in the bin is enhanced by providing a bin whose generally horizontally disposed lower wall is comprised of oppositely inclined nonhorizontal portions. The entrance portion and the back portion of the bin are both generally inclined upward, to form a quasi curved or concave surface which faces upward. This concave surface which, if it were circular, is formed about an axis generally normal to the direction of sheet travel. A limitation of the present invention is that the generally concave shape of the bottom of each collator bin is somewhat greater than the curvature to be expected by the curling of the sheets due to the printing process. As a result, if the paper resides in the bin with the leading and trailing edges of the sheets curled down, these edges engage the bottom surface of the bin in line contact and tend to "break the back" of the sheet. Thus, the leading edge of the next sheet to be inserted in the bin does not encounter the upturned edge of the sheets already within the bin, this being the condition most likely to cause a sheet jam. The other condition of possible sheet stacking is wherein the sheets enter the bin curled upward. In this case, since the curvature of the collator bin is greater than that of the paper, the leading and trailing sheet edges again engage the bottom of the bin in line contact. The back of the bent sheet is again broken and the sheets reside in the tray with their trailing and leading edges tightly packed, so as to avoid interference with the leading edge of the sheet subsequently to be stacked in the bin.
As can be appreciated, this invention is of particular utility when grain-long cut sheets are fed in the direction of their shortest dimension, such that the tendency to curl results in a generally curved quasi cylindrical surface formed about an axis normal to the direction of sheet travel.
As a result of this unique construction, apparatus functioning in accordance with the teachings of the present invention have succeeded in stacking as many as 100 sheets into a bin having vertical height of approximately 1.3 inches.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing.